The present invention relates generally to lens cleaning compositions and methods of use. More specifically, this invention is concerned with new enzyme cleaners and methods for effective removal of film build-up and debris from contact lenses which may be present as proteinaceous-carbohydrate-lipid containing deposits.
Cleaning compositions for contact lenses generally fall into one of three categories: surfactant cleaners; oxidative cleaners and enzyme cleaners. Surfactant cleaners are widely used, for example, by placing a drop of solution on a lens, rubbing the lens between the fingers followed by rinsing. Although such cleaners are usually safe and not harmful to lenses when used properly, most surfactant cleaners are not effective in the removal of protein deposits.
The second type of cleaning system involves oxidative products containing, for example, persulfates and perborates. They may be used either by cold soaking or with boiling for about 30 minutes. This type of cleaning system is mainly effective in removing non-protein deposits from contact lenses. They are generally non-toxic, ; however, oxidizing agents can have a deleterious effect on lenses. One possible explanation is that they may oxidize the basic polymer chain by the introduction of pH-sensitive molecular groups.
The third method of cleaning is with enzymes. Enzyme cleaners are generally viewed as being efficacious, safe and capable of removing the principal component of contact lens film and debris, namely protein. Some also have the ability to remove carbohydrate and lipid deposits from contact lenses.
Heretofore, the supply of proteolytic, carbolytic and lipolytic enzymes e.g. . . . proteases, amylases and lipases for use in contact lens cleaning solutions was restricted to plant and animal sources. Cleaning solutions prepared from plant and animal derived enzymes have several shortcomings. In most instances, they either impart an unpleasant odor to the cleaning bath or develop an odor after a few hours of use. In some cases, plant and animal proteases and amylases will discolor lenses.
Contact lens cleaning solutions prepared with plant and animal derived proteases like papain, chymopapain, pancreatin, trypsin, chymotrypsin, pepsin, ficin, carboxypeptidase, aminopeptidase, and bromelin are described in several patent publications e.g. . . . U.S. Pat. No. 3,910,296; U.K. Patent Publication GB No. 2,088,851; Japanese application No. 113,233 published May 31, 1975 as Kokai 64,303 and U.S. Pat. No. 4,096,870. In addition to the patent citations, enzymatic lens cleaners prepared with proteases from pork, namely pancreatin have been commercially available from Alcon Laboratories. Enzymatic contact lens cleaners prepared with plant proteases i.e. papain have also been available from Allergan Pharmaceuticals under the registered trademark Soflens Enzymatic Cleaning Tablets. Although these preparations are generally effective in cleaning contact lenses, they have shortcomings in addition to those previously mentioned. That is, besides the propensity for unpleasant odors and potential for discoloring lenses, cleaners containing proteases like pancreatin from pork or beef can induce an allergic response among some users. In addition, solutions containing pancreatin have a tendency to become cloudy and turbid.
Plant proteases, for example papain, normally require lengthy cleaning cycles ranging from 4 to 12 hours in order to remove film and debris from lenses. Such lengthy cycles can be an inconvenience to the user. In addition, cleaning solutions prepared with plant and animal proteases require the application of heat e.g. 80.degree. C. which is needed not only to disinfect the lenses, but also to inactivate the enzyme.
Contact lens cleaners containing enzymes also require stabilizers/activators. For example, papain requires cysteine. Pancreatin requires calcium salts. Without the use of an activator papain and other similar plant enzymes will remain dormant. Activators like cysteine are hygroscopic and have a tendency to pick-up moisture creating manufacturing difficulties. Such enzyme products can only be manufactured and packaged under stringent standards to eliminate any moisture from entering the packaging otherwise it will autoreact and shorten the shelf life of the cleaner.
Microbial proteases derived from Bacillus and Streptomyces bacteria and Aspergillus mold have been previously described. U.S. Pat. No. 3,590,121 discloses an effervescent tablet used for making mouthwash. The tablets and solutions of this patent employ a neutral protease referred to as a metallo-enzyme having an optimum activity at a pH of 6 to 8. Because metals are an integral part of the enzyme, its activity is inhibited by the presence of chelating agents which are customarly employed in contact lens cleaning preparations to bind calcium and other unwanted metals from reacting with proteins and depositing on lenses. Consequently, enzymes which are inhibited by chelating agents, like those described in U.S. Pat. No. 3,590,121 are generally unsatisfactory for use with contact lenses.
U.S. Pat. No. 3,717,550 describes the preparation of liquid concentrates of bacterial protease and/or amylase. The liquid concentrates are used for making such products as household detergents.
Accordingly, there is a need for safer, more dependable enzyme cleaning preparations which will offer a broad spectrum of cleaning capability for efficient removal of at least protein and carbohydrate films and debris from contact lenses. The enzymes should be both stable in solution, remain active at elevated temperatures and be compatible with other components of the cleaning composition. Preferably, the enzyme system should not depend on the use of activators which may lead to autodigestion with the enzyme, limiting the shelf-storage life. Similarly, the cleaning process should be convenient for the user eliminating the need for protracted soaking periods by allowing the user the flexibility of shorter cleaning times. The enzyme cleaning composition should also be free or substantially free of odor and not cause discomfort to the wearer when the lenses are reinserted into the eyes. They should not cause irritation or allergic response as a result of residual amounts of enzyme on the lens surface.